Analysis of reproducibility of 2D Ultrasound imaging with transient ShearWave Elastography on spastic gastrocnemius medialis muscle in children with spastic hemiplegic cerebral palsy

PurposeThe aim of the study was to assess the intra- and inter-operator reliability of pennation angle (PA) and muscle thickness (MT) 2D measurements and of shear elastic measurement, using ultrasound imaging (US). Those measurements were realised on spastic gastrocnemius medialis muscle at rest and at maximal passive stretching, in children with spastic hemiplegic cerebral palsy. The paretic side measurements were compared to the non-paretic side.Material and methodsEight patients took part in 2 inter-session reliability experiments, realised at a 7days interval by two different operators. The Aixplorer® Supersonic US scanner with the transient ShearWave Elastography (SWE) software was used. The stretching experiments were made manually and controlled by a goniometer.ResultsThe intra-operator reliability of the 2D measurements was good. Both operators found a coefficient of variation (CV)≤7% and 6.04% for MT at rest and at maximal passive stretching respectively,≤9.77% for PA at rest. The reliability of the shear elastic modulus measurement in the sagittal plane was only good at rest for both operators with a CV≤9.82%, versus 25.29% at stretching. The inter-operator reliability of 2D measurements was good for MT exclusively (CV≤9.69% for the two sessions and two operators). At rest, MT was weaker in the paretic side (10.17±1.52mm) versus non-paretic side (12.43±2,85mm) (P<0.0001), and the shear elastic modulus was stronger in the paretic side versus non-paretic side (29.45±5.7Kpa vs 23.77±3.93Kpa) (P